Despite extensive medical treatment, surgical resection is required in approximately 70%-80% of the patients at some time. However, recurrence of the disease after operation occurs in the vast majority of patients and is a serious limitation of surgical management. In this setting the bacterial flora plays an important role as demonstrated by the benefit of postoperative antibiotic therapy with either metronidazole or ornidazole or the absence of inflammation in patients with diverting ileostomy. However, both aforementioned antibiotic regimens have numerous adverse events limiting the value of this therapy in daily clinical practice. Ciprofloxacin suppresses Gram negative aerobic bacterial species, including enteroadherent/invasive E. coli strains, which are increased in early and chronic ileal lesions of Crohn's disease patients. A limited number of clinical data suggest efficacy of this drug in patients with established Crohn's disease. This exploratory multicenter prospective, placebo-controlled trial performed at 9 experienced IBD centers will analyze the safety and tolerability of a 6 months therapy with ciprofloxacin compared to placebo in 40 patients (randomly assigned in a 1:1 ratio) undergoing ileocecal resection with primary anastomosis. No other treatments for Crohn's disease will be permitted. The primary objective of this study is to assess the safety and tolerability of 6 months therapy of ciprofloxacin (500 mg bid) vs. placebo tablets for prevention of endoscopic recurrence in postoperative Crohn's disease patients. The secondary objectives of this study are to evaluate the rate of endoscopic recurrence in the neoterminal ileum and at the ileocolonic anastomosis as well as the extent of colonic lesions. Additionally biopsy samples at the anastomotic site and patient DNA and serology samples will be collected for later analysis of bacterial ribosomal 16S DNA, bacterial antibodies and DNA polymorphisms (such as NOD2, OCTN/1/2, ATG 16L1 or IL-23 receptor). The clinical data generated by this study will serve as a basis for a definitive clinical trial investigating the effectiveness of ciprofloxacin in the prevention of endoscopic recurrence in postoperative Crohn's disease. [unreadable] [unreadable] [unreadable]